Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

Scientific Investigations Report 2017–5003

U.S. Department of the Interior U.S. Geological Survey Cover. Viable lake whitefish eggs collected from the Detroit River. Photograph by U.S. Geological Survey Great Lakes Science Center staff. Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

By Carson G. Prichard, Jaquelyn M. Craig, Edward F. Roseman, Jason L. Fischer, Bruce A. Manny, and Gregory W. Kennedy

Scientific Investigations Report 2017–5003

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2017

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Suggested citation: Prichard, C.G., Craig, J.M., Roseman, E.F., Fischer, J.L., Manny, B.A., and Kennedy, G.W., 2017, Egg deposition by lithophilic-spawning fishes in the Detroit and Saint Clair Rivers, 2005–14: U.S. Geological Survey Scientific Investigations Report 2017–5003, 20 p., https://doi.org/10.3133/sir20175003.

ISSN 2328-0328 (online) iii

Acknowledgments

We thank Rose Ellison from the U.S. Environmental Protection Agency, Jen Read and Lynn Vaccaro of the University of Michigan Water Center, and Mike Thomas of the Michigan Depart- ment of Natural Resources for their support with this research. Jim Boase and Justin Chiotti of the U.S. Fish and Wildlife Service Alpena Fisheries Conservation Office and Rich Drouin of the Ontario Ministry of Natural Resources and Forestry provided logistical support for various stages of field work. We acknowledge the efforts of numerous field technicians, graduate students, and interns who assisted with this work. Stacey Ireland and three anonymous reviewers provided useful comments that greatly improved the quality of this manuscript. This is Scientific Investi- gations Report 2017–5003 of the USGS Great Lakes Science Center. This work was funded by the Great Lakes Restoration Initiative Project #70–Fish Habitat Enhancement Strategies for the Huron–Erie Corridor and the USGS Science Support Program Project 10–R3–04. iv

Contents

Abstract...... 1 Introduction...... 1 Methods...... 3 Study Location...... 3 Fish Egg Sampling...... 3 Data Analyses...... 4 Results ...... 6 Detroit River...... 6 Saint Clair River...... 13 Discussion...... 15 Summary...... 17 References Cited...... 17

Figures

1. Map showing location of the Saint Clair–Detroit River System identifying major landmarks and metropolitan areas...... 2 2. Maps showing egg sampling locations on the Saint Clair and Detroit Rivers...... 5 3. Bar chart showing average duration of egg collections of lithophilic-spawning fishes in the Detroit and Saint Clair Rivers for years in which the onset and cessation of spawning were detected...... 10 4. Cumulative mean catch-per-unit effort of eggs on mats sampled on or near the artificial reef complex off the northeastern shores of A, Belle Isle 2005–14;  and B, Fighting Island 2006–14...... 11 5. Cumulative mean catch-per-unit effort of eggs on mats sampled in the vicinity of the artificial reef complex at the head of Fighting Island...... 12 6. Densities of eggs collected 2010–14 at five regions sampled each year in the Saint Clair River...... 14

Tables

1. Median cumulative catch–per–unit effort of walleye eggs collected during spring egg mat sampling in the Detroit River, 2005–14...... 6 2. Median cumulative catch–per–unit effort of sucker eggs collected during spring egg mat sampling in the Detroit River, 2005–14...... 7 3. Median cumulative catch–per–unit effort of trout–perch eggs collected during spring egg mat sampling in the Detroit River, 2005–14...... 8 4. Median cumulative catch–per–unit effort of lake whitefish eggs collected during fall egg mat sampling in the Detroit River, 2006–14...... 8 5. Water temperatures corresponding to the onset and cessation of egg collections in the Detroit River, 2005–14...... 9 6. Water temperatures corresponding to the onset and cessation of egg collections in the Saint Clair River, 2010–14...... 14 v

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain Length centimeter (cm) 0.394 inch (in) meter (m) 3.28 foot (ft) kilometer (km) 0.621 mile (mi) Area hectare (ha) 2.47 acre square meter (m2) 10.8 square foot (ft2) hectare (ha) 0.00386 square mile (mi2) Volume cubic meter (m3) 35.3 cubic feet (ft3) Flow rate meter per second (m/s) 3.28 foot per second (ft/s) cubic meter per second (m3/s) 35.3 cubic foot per second (ft3/s) Mass kilogram (kg) 2.20 pound (lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32

Abbreviations

CPUE catch-per-unit effort GLSC Great Lakes Science Center SCDRS Saint Clair-Detroit River System USGS U.S. Geological Survey Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

By Carson G. Prichard, Jaquelyn M. Craig, Edward F. Roseman, Jason L. Fischer, Bruce A. Manny, and Gregory W. Kennedy

Abstract SCDRS including walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), cisco (Coregonus artedi), and A long-term, multiseason, fish egg sampling program lake sturgeon (Acipenser fulvescens) (Goodyear and others, conducted annually on the Detroit (2005–14) and Saint Clair 1982) that all contributed to a thriving commercial fishery (2010–14) Rivers was summarized to identify where produc- (Baldwin and others, 2009); however, habitat changes from tive fish spawning habitat currently exists. Egg mats were over a century of shipping channel excavation and dredging, placed on the river bottom during the spring and fall at historic shoreline development, and pollution cumulatively resulted in spawning areas and candidate fish spawning habitat restora- huge losses of fish spawning and nursery habitats (Edsall and tion sites throughout both rivers. Widespread evidence was others, 1988; Manny and others, 1988; Bennion and Manny, found of lithophilic spawning by numerous native fish species, 2011). These perturbations, in combination with heavy com- including walleye (Sander vitreus), lake whitefish Coregonus( mercial fishing pressure, led to large-scale losses of fish popu- clupeaformis), lake sturgeon (Acipenser fulvescens), suckers lations in these rivers, including the local extirpations of cisco (Catostomidae spp.), and trout-perch (Percopsis omiscomaycus). and lake trout (Salvelinus namaycush) (Smith, 1972), the near extirpation of lake whitefish (Smith, 1915, 1917; Roseman Walleye, lake whitefish, and suckers spp. spawned in nearly and others, 2007), and declines in walleye (Manny and others, every region of each river in all years on both reef and nonreef 2010) and lake sturgeon (McClain and Manny, 2000; Manny substrates. Lake sturgeon eggs were collected almost exclu- and Kennedy, 2002). Although the extents to which over- sively over constructed reefs. Catch-per-unit effort of wall- fishing, habitat alterations, and pollution contributed to the eye, lake whitefish, and sucker eggs was much greater in the declines of each species likely vary, perpetual habitat modi- Detroit River than in the Saint Clair River, while Saint Clair fications that succeeded their declines currently inhibit their River sites supported the greatest collections of lake sturgeon recovery to former levels of abundance (Hondorp and others, eggs. Collections during this study of lake sturgeon eggs on 2014). Specifically, the lack of suitable spawning habitat limits man-made spawning reefs suggest that artificial reefs may be the restoration of lake sturgeon (Manny and others, 2005) and an effective tool for restoring fish populations in the Detroit likely other lithophilic-spawning fishes in the SCDRS. and Saint Clair Rivers; however, the quick response of lake Since 2004, the Saint Clair–Detroit River System Initia- sturgeon to spawn on newly constructed reefs and the fact that tive has coordinated research and management efforts towards walleye, lake whitefish, and sucker eggs were often collected science-based restoration of environmental services within over substrate with little interstitial space to protect eggs from the SCDRS and the Great Lakes Basin (http://www.scdrs. siltation and predators suggests that lack of suitable spawning org). This initiative is a binational partnership of Federal, habitat may continue to limit reproduction of lithophilic- State, provincial, academic, First Nations, and private sector spawning fish species in the Saint Clair-Detroit River System. entities whose primary objective is restoring functional fish spawning habitat. The SCDRS Initiative required contempo- rary information on the locations of functional fish spawning Introduction habitat throughout the SCDRS to direct restoration efforts to areas where (1) new habitat may be most effective, and (2) the The Saint Clair-Detroit River System (SCDRS) is the deleterious effects of altering habitats presently supporting fish 148-kilometer (km) long waterway connecting Lakes Huron, spawning may be avoided. Saint Clair, and Erie and forms a portion of the international Little direct evidence of fish egg deposition in the border between Canada and the United States (fig. 1). At the SCDRS exists. Of the 28 native species that historically turn of the 20th century, 28 native fish species spawned in the spawned in the SCDRS, most spawned in tributaries to the 2 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

Lake Huron N N Lake Blue Water Bridge Belle Isle Saint Clair

Port Huron Sarnia Detroit Peche Island

Fort Wayne Marysville

Stag Island Zug Island Reef Windsor

Fighting Island Detroit River Grassy Island St. Clair Wyandotte

Fighting Island Channel MICHIGAN Grosse Ile ONTARIO Trenton Fawn Island Saint Clair River Stony Island Coal cinder pile Sugar Island

Amherstburg Algonac Amherstburg Channel Lake Erie Bois Blanc Island Livinstone Channel Celeron Island North Channel Shipping Channel Middle Channel Lake Erie Lake Saint Clair 0 5 KILOMETERS 0 5 KILOMETERS

0 5 MILES 0 5 MILES

Figure 1. Location of the Saint Clair–Detroit River System identifying major landmarks and metropolitan areas. system or in the more lentic, nearshore areas (Goodyear the commercial fishery for lake whitefish quickly collapsed and others, 1982); in contrast, walleye, lake whitefish, and and spawning runs of lake whitefish into the Detroit River lake sturgeon were reported by Goodyear and others (1982) disappeared (Bennion and Manny, 2011). Lake whitefish eggs to spawn in the deeper flows of the main channels of both have never been reported from the Saint Clair River, although rivers. Muth and others (1986) were the first to document several studies have recorded low densities of their larvae in walleye eggs in both rivers in a large-scale effort to character- that river (Goodyear and others, 1982; Hatcher and Nester, ize the abundance and distribution of fish eggs and larvae in 1983; Leslie and Timmins, 1991). It was not until the collec- the SCDRS; however, lake whitefish and lake sturgeon were tion of lake whitefish adults and eggs in the Detroit River by not among the 18 other species whose eggs were identified. Roseman and others (2007, 2012) that this species’ presence in Since Muth and others (1986), there have been no published the SCDRS was confirmed for the first time since the mid-20th accounts of walleye or lake whitefish eggs in the Saint Clair century when lake whitefish populations in the river collapsed River, although eggs of both species have been consistently (Baldwin and others, 2009). observed in the Detroit River (Manny and others, 2007, 2010; Lake sturgeon populations in the Great Lakes are listed as Roseman and others 2007; Roseman, Boase, and others 2011; threatened by the Michigan and Ontario governments (Manny Roseman, Manny, and others 2011). and Mohr, 2013), meaning they are likely to become endan- Lake whitefish once supported the largest commercial gered if factors threatening them are not addressed. In the fishery in the SCDRS. Landings averaged 64.5 thousand SCDRS, lake sturgeon are known to actively spawn on natural kilograms (kg) in the SCDRS from 1871 to 1917, with a peak substrate at the head of the Saint Clair River in the vicinity of harvest of 451.8 thousand kg in 1874 (Baldwin and others, the Blue Water Bridge (fig. 1; Manny and Kennedy, 2002); 2009). Following the construction of the Fighting Island however, prior to the construction of modern artificial reefs in Channel (1914–15) that extended from shoal areas at the base the Saint Clair River, the only other lake sturgeon spawning of Fighting Island to the east side of Grassy Island (fig. 1), activity that had been documented was on a residual bed of Methods 3 coal cinders in the North Channel Saint Clair River (Manny Areas of Concern have been designated by the International and Kennedy, 2002; Nichols and others, 2003; Thomas and Joint Commission, and 14 Beneficial Use Impairments have Haas, 2004; Bouckaert and others, 2014). This man-made been identified by the U.S. Environmental Protection Agency, spawning site was likely formed in the late 1800s by the including the losses of fish and wildlife habitat and degrada- offloading of spent coal by coal-burning vessels (Thomas and tion of fish and wildlife populations (Manny, 2003; Great Haas, 2004). The spawning of lake sturgeon in the Detroit Lakes Water Quality Agreement, 2013). River was considered unknown until 2001 when Caswell and The Saint Clair River is the upper 65 km of the SCDRS. others (2004) collected eggs from another residual coal cinder It connects Lake Huron to Lake Saint Clair and has a mean bed offshore of Zug Island. Prior to 2001, no lake sturgeon discharge of 5,150 cubic meters per second (m3/s) (Liu and eggs had been collected on any natural substrates sampled in others, 2012). The river has few islands in the upper and the Detroit River. middle sections but forms a large delta that serves as an Lake sturgeon spawning on the residual coal cinder beds important nursery area for fishes (Edsall and others, 1988). in both rivers provided evidence that artificial substrates can The habitat alterations which are due to the formation and support lithophilic fish spawning in the SCDRS. This finding, maintenance of shipping channels began in 1855 and contin- and additional reports of successful spawning by lake sturgeon ued regularly through the mid-20th century. Most notable was on artificial spawning substrates in other large rivers (Bruch the excavation of a shipping channel (213 m wide × 8.2 m and Binkowski, 2002; Johnson and others, 2006; Dumont and deep) in 1959 that extended 9.7 km through the southeastern others, 2011), prompted reef construction projects at Belle bend of the river. This project alone involved the removal of Isle (2004) and Fighting Island (2008) in the Detroit River approximately 18.2 million cubic meters (m3) of sand and clay (Manny, 2006; Manny and others, 2015) and in the Middle (Larson, 1995). Channel Saint Clair River (2012) and at Pointe aux Chenes The Detroit River is the lower 44 km of the SCDRS. It (2014) near Algonac, Michigan, in the Saint Clair River connects Lakes Saint Clair and Erie and has a mean discharge (Read and Manny, 2014; Manny and others, 2015) to address of 5,300 m3/s (Derecki, 1984). The river is heavily altered; restoration needs. Combined, these projects created new, rocky approximately 87 percent of the Michigan shore is lined substrate over 8,400 square meters (m2) of river bottom in with concrete or steel bulkheads, and less than 3 percent of areas with suitable physical condition; for example, current the coastal wetlands historically adjacent to the river still velocities ≥0.5 meter per second (m/s), depth greater than the exist (Manny, 2003); additionally, a network of deep (greater photic zone of about 4.5 meters (m), and sufficient distance than 10 m) shipping channels runs the length of the river from shipping channels (Bennion and Manny, 2014) . Spawn- (Manny and others, 1988). Habitat alteration from excava- ing responses of lake sturgeon and other fish species to these tion and maintenance of these channels in the Detroit River artificial spawning beds has been monitored with an intensive has been more extensive than in the Saint Clair River. At least egg sampling program started by the U.S. Geological Survey 46.2 million m3 of material have been dredged or excavated Great Lakes Science Center (USGS–GLSC) since the onset of from the river, the spoils of which now cover an additional the restoration program. 4,050 hectares (ha) of river bottom (Bennion and Manny, The primary objective of this report is to summarize 2011). The Livingstone Channel, which was dredged through the areal extent of lithophilic-spawning fish egg collections a shallow bedrock sill, is the largest of these channel projects in the Detroit (2005–14) and Saint Clair (2010–14) Rivers. and concentrated a majority of the discharge from the Detroit The dates and water temperatures at the onset and cessation River into a singular outflow into Lake Erie (Bennion and of spawning for the primary taxa are also described. These Manny, 2011). Twelve large islands exist in the Detroit results depict contemporary use of naturally occurring and River—many of these in the lower reaches comprise parts man-made spawning habitats by lithophilic-spawning fishes in of the more than 2,300 ha in the Detroit River International the SCDRS. The confines of egg mat sampling methods and Wildlife Refuge (Hartig and others, 2010). Despite the degree considerations for future research also are discussed. to which the Detroit River has been modified, the islands and refuge remain some of the most biologically diverse regions in North America (Bull and Craves, 2003). Methods Fish Egg Sampling Study Location Furnace filter egg mats (38 × 50 × 2.5 centimeters [cm] The study area encompasses the full lengths of the Detroit wrapped around a 38 × 24 × 0.5-cm metal frame) placed on and Saint Clair Rivers (fig. 1). Among the major rivers of the the river bottom were used to assess fish egg deposition. Egg Great Lakes, these two connecting channels are exceptional sampling was conducted typically from mid-March through in that they remain free of barriers; however, the SCDRS is June, from ice-out until eggs were no longer collected, and an ecosystem that is heavily impacted by human activities again from mid-October through mid-December, when ice (Hondorp and others, 2014). Throughout the ecosystem, two cover prevented further egg sampling. Methods for egg mat 4 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14 design, deployment, and retrieval are summarized by Rose- and sites randomly distributed throughout the river (Roseman man, Boase, and others (2011). Generally, egg mat gangs for and others, 2012) was conducted in fall 2006–7. An average a given site consisted of 3 to 12 egg mats that were deployed of 30 sites per year were sampled from Peche Island down- early in the season and checked weekly thereafter for the pres- stream to Sugar and Celeron Islands, providing a preliminary ence of fish eggs. Earlier survey years employed the buoyed inventory of primary lake whitefish spawning areas in the egg mat sampling strategy described by Nichols and others Detroit River. Fall sampling efforts were reduced to NE (2003). In subsequent years, a buoy-less design was used in Fighting Island and Belle Isle (2010) or restricted to only NE which sampling sites were identified and revisited using the Fighting Island (2009, 2011), mostly because of constraints Global Positioning System (Roseman, Boase, and others, on financial and personnel resources associated with the 2011). After retrieval, all eggs were carefully removed with addition of the Saint Clair River fish egg sampling program forceps and counted, and egg mat gangs were redeployed in that began in 2010. With the areal extent of lake whitefish the same location. All eggs removed from the egg mats were spawning generally inventoried, fall sampling during 2012–14 identified based on size, color, transparency, oil globule posi- targeted sites favored by lake whitefish with a more long-term tion (Auer, 1982), and timing of spawning. In general, eggs monitoring focus. were identified by the naked eye and categorized as walleye, Spring and fall sampling from the Saint Clair River began suckers (Catostomid species [spp.]), trout-perch (Percopsis in 2010 and is still being conducted. In the springs of 2010 omiscomaycus), or lake sturgeon in the spring, and as lake and 2011, an average of 26 sites were sampled that targeted whitefish in the fall. For confirmation, subsets of eggs were known and historically important walleye and lake sturgeon taken to the GLSC to be hatched following Sutherland and spawning areas (Goodyear and others, 1982). Sampling sites others (2014); the larval fish were then identified following were located from the outlet of Lake Huron to the downstream Auer (1982). Eggs of round goby (Neogobius melanostomus) ends of the North, Middle, and Main Shipping Channel Saint and Morone spp. (that is, white bass [Morone chrysops] and Clair River. Similar to Detroit River efforts, spring sampling white perch [Morone americana]) were noted when present in the Saint Clair River from 2012 to 2014 was reduced to but were not counted because of their small size, high densi- monitoring sites identified in the previous 2 years as fish ties, and the lengthy amount of time to process and remove spawning areas as well as preassessment and postassessment their eggs from the egg mats. of the Middle Channel Saint Clair River reefs, which were Fish egg sampling from the Detroit River began in the constructed in June 2012. Fall sampling efforts from the Saint spring of 2005 following construction of the Belle Isle spawn- Clair River have remained relatively consistent, averaging ing reefs (Manny, 2006) and was conducted annually through 22 sites per year from 2010 to 2014. 2014. In 2007, the egg sampling program was expanded to 19 sites as an exploratory assessment of lithophilic spawning, targeting historically important walleye and lake sturgeon Data Analyses spawning grounds from Belle Isle downstream to Sugar and Celeron Islands (fig. 1). In spring 2008, the river-wide Cumulative catch-per-unit effort (CPUE) of eggs sampling regime was expanded, and an additional 10 sites collected per species per spawning season was calculated were sampled offshore of the northeast (NE) shore of Fighting and reported by river regions, which are composed of pooled Island (NE Fighting Island) where an artificial fish spawning sampling sites (fig. 2). Cumulative CPUE was derived by reef was subsequently constructed that summer (Roseman, summing all the eggs sampled per gang at each site for a given Manny, and others, 2011). Sampling efforts in spring 2009 year and dividing by the number of mats fished. Because of were restricted to postassessment of the Fighting Island reef the influences of water velocity and substrate complexity on project. Sampling was expanded in 2010 to again include egg transport and retention (Jason L. Fischer, U.S. Geological Belle Isle sites. With the exception of 2012, when only sites Survey, unpublished data, 2016), it is unlikely that catchability at NE Fighting Island were sampled, years 2011–14 con- is equal between egg mats and the river bottom; therefore, egg stituted a long-term monitoring approach whereby sites at data in this report are reported as CPUE instead of egg density Belle Isle, a nearshore debris mound adjacent to Joe Louis per unit area, and readers are cautioned against extrapolating Arena, NE Fighting Island, offshore of the northwest (NW) egg densities on mats to egg densities on the river bottom. shore of Fighting Island (NW Fighting Island/Grassy Island), Mean cumulative CPUEs and their associated standard northern Livingstone Channel, Hole-in-the-Wall (a break in errors were calculated on the natural log (loge) scale under the the dike of the Livingstone Channel), and Sugar Island were assumption that egg densities followed a lognormal distribution consistently revisited. among sampling sites within a given region. Direct compari- Fall sampling targeting lake whitefish eggs from the sons of egg CPUEs among years should be made with some Detroit River began in 2006 following the discovery of adult caution as not all sites were sampled each year, and sites were lake whitefish and eggs (Roseman and others, 2007) and added or removed. Every effort was made to present these incidental catches in early spring 2006 at Belle Isle of hatch- data in such a way that statistical biases were not introduced ready lake whitefish eggs. Exploratory sampling of historic because of heterogeneity in the spatial and temporal scope of lake whitefish spawning sites (Goodyear and others, 1982) the dataset; finally, because means of loge-transformed data Methods 5

EXPLANATION Lake Huron A Region B N N A. Lake Huron/Head of St. Clair River B B. Port Huron C C. Stag Island (upper) A D. Stag Island (lower) Detroit River E. Saint Clair Middle Grounds C F. Fawn Island E D G. Algonac D H. North Channel (Deep hole) EXPLANATION F Region I. North Channel (Midway) G J. Middle Channel (Reef) A. Peche Island E K. Coal cinder pile B. Belle Isle L. North Channel (End)/ C. Debris mount adjacent to Chenal A Bout Rond H Joe Louis Arena I M. Middle Channel (End) D. Fort Wayne N. Lower Main Shipping Channel F E. Zug Island F. NE Fighting Island K G. NW Fighting Island/Grassy Island J Saintt Clair River H. SW Fighting Island/NE Grosse Ile I. SE Fighting Island J. North Livingstone Channel Lake Saint K I H Clair L L K. Trenton Channel G N M L. Bois Blanc Island/Hole-in Wall J M. Sugar Island M N N. Celeron Island Lake Erie

0 5 KILOMETERS 0 5 KILOMETERS

0 5 MILES 0 5 MILES

Figure 2. Egg sampling locations on the Saint Clair and Detroit Rivers. represent median values on the original scale of the data, Rearing of collected sucker eggs in the laboratory and

CPUEs were reported as mean values on the loge scale and as identifying the hatched larvae has revealed that small sucker median values when back transformed from the loge scale to eggs are Carpiodes spp. (quillback [Carpiodes cyprinus] or the scale of the data. river carpsucker [Carpiodes carpio]) and large sucker eggs are Dates and water temperatures of onset and cessation of either white sucker (Catostomus commersonii) or northern hog spawning are presented for the primary taxa observed in each sucker (Hypentilium nigricans) (Jaquelyn M. Craig, U.S. Geo- river. Surface-water temperatures were measured using the logical Survey, unpublished data, 2016). Because collected onboard electronic sensor. In many cases, eggs were collected sucker eggs likely represent at least four species that cannot during the first or last week of sampling. If greater than be readily discriminated during early life history stages, the 5 percent of the total eggs collected in a given year for a given resolution of the analyses of sucker eggs is limited to either taxon were collected during the first or last week of sampling, small or large, or all sucker eggs in aggregate. it was concluded that the onset or cessation of spawning, Egg mats are a tool for documenting spawning activity respectively, was missed. Otherwise, spawning onset dates in large, deep rivers where other sampling methods are not were estimated as the first egg mat set date for which greater feasible. While an important tool for assessing egg deposition, than 2.5 percent of the total eggs collected for each taxon were egg mats have some limitations. Eggs may become dislodged observed. Similarly, spawning cessation dates were estimated from mats, may be transported from upstream spawning as the first egg mat pull date for which greater than 97.5 percent activity, and may hatch or be predated upon between deposi- of the total eggs collected for each taxon were observed. Thus, tion and egg mat retrieval; thus, egg CPUEs are provided only the reported onset and cessation dates and water temperatures as an index of abundance, and standard errors of egg CPUEs conservatively describe at least 95 percent of the egg deposi- are depicted to describe the variability in the data. Focusing tion for a given taxon in a given year. Note that in spring 2012, on the objective of summarizing the sampling program and sampling in the Detroit River only occurred from April 24 contemporary egg deposition of lithophilic-spawning fishes to May 15; therefore, conclusions were not made regarding in the system, refrainment from statistical comparisons of egg the onset and cessation of spawning of any species except CPUEs was exercised (unless noted), and a detailed consider- lake sturgeon. ation of the aforementioned uncertainties was provided in the 6 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

“Discussion” section of the report. Descriptive phrases such 849 eggs/mat in 2013). Other notable high densities of walleye as “was greater than” or “did not differ” are based solely on eggs were observed at Fort Wayne in 2007 (124 eggs/mat) interpretation of the observed egg CPUEs and their associated and 2013 (778 eggs/mat), as well as at Zug Island in 2011 standard errors. (111 eggs/mat), and at Sugar Island in 2013 (103 eggs/mat). Collections of small and large sucker eggs were also widespread throughout the Detroit River each year. Large sucker eggs were observed slightly more frequently, being Results collected in 31 of 50 year-region combinations, whereas small sucker eggs were observed in 29 of 50 year-region combina- Detroit River tions. Sucker eggs were observed in at least one year from every region that was sampled except the nearshore debris Among all the years sampled, walleye were the most mound adjacent to Joe Louis Arena, SW Fighting Island/NE prolific lithophilic-spawning fish species, both in terms of Grosse Ile, and Celeron Island. Overall, peak combined sucker areal extent of egg deposition and in CPUE of eggs collected. egg CPUEs in a given spring were much lower than those Walleye eggs were caught in all regions of the river each of walleye, ranging from less than 1 percent of walleye egg spring, with the exception of the Trenton Channel in 2007. CPUEs in 2011 to 23 percent in 2006 when only Belle Isle Walleye egg CPUEs were greatest in the vicinity of NW Fight- was sampled. However, local sucker egg CPUEs occasionally ing Island/Grassy Island and at Bois Blanc Island/Hole-in-the- exceeded those of walleye, and this was observed at SE Wall, where median cumulative egg CPUEs peaked in 2013 at Fighting Island (2007), Zug Island (2008) and NE Fighting 1,593 and 5,902 eggs/mat, respectively (table 1). Bois Blanc Island (2008 and 2014). Among years where a majority of the Island/Hole-in-the-Wall supported the greatest walleye egg regions were sampled, the NE Fighting Island region ranked CPUEs in 4 of the 5 years in which it was sampled. Further first or second in 4 out of 5 years (table 2). The greatest sucker upstream, high egg CPUEs were consistently observed at egg CPUEs were observed at NE Fighting Island in 2013 Belle Isle (peaking at 310 eggs/mat in 2011) and the near- (57.7 eggs/mat) and 2014 (60.9 eggs/mat). Other relatively shore debris mound adjacent to Joe Louis Arena (peaking at large cumulative CPUEs of sucker eggs were observed at

Table 1. Median cumulative catch–per–unit effort (CPUE) of walleye eggs collected during spring egg mat sampling in the Detroit River, 2005–14. Italics denote sampling season ended early because of gear loss and values may be underestimated.

[–, site was not sampled]

Region Walleye CPUE (eggs/mat)—Detroit River (in downstream order) 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Peche Island – – – 45 – – – – – – Belle Isle 29 9.4 99 263 – – 310 – 290 32 Debris mound adjacent – – – – – – 293 – 849 – to Joe Louis Arena Fort Wayne – – 124 14 – – – – 778 – Zug Island – – 111 5.0 – – – – – – NE Fighting Island – – 33 4.8 98 14 43 11 115 31 NW Fighting Island/ – – 132 45 – – 735 – 1,593 1,073 Grassy Island SW Fighting Island/ – – 7.3 3.1 – – – – – – NE Grosse Ile SE Fighting Island – – 0.33 1.0 – – – – – – N Livingstone Channel – – 8.3 1.7 – – 3.3 – 365 47 Trenton Channel – – 0 4.0 – – – – – – Bois Blanc Island/ – – 350 137 – – 2,584 – 5,902 2,735 Hole–in–Wall Sugar Island – – 49 14 – – 18 – 103 2.0 Celeron Island – – 7.7 – – – – – – – Results 7

Zug Island in 2008 (15.0 eggs/mat) and NW Fighting Island/ Trout-perch eggs were collected in the spring across a Grassy Island in 2011 (16.1 eggs/mat). Although large sucker broad spatial and temporal extent. They were observed at eggs were observed most often, the greatest sucker egg CPUEs NE Fighting Island (7 of 8 years sampled), Belle Isle (4 of tended to be comprised mostly of small sucker eggs. 8 years), Bois Blanc Island/Hole-in-the-Wall (4 of 5 years), Lake sturgeon eggs were only observed following the Sugar Island (2 of 5 years), and NW Fighting Island/Grassy 2008 construction of an artificial spawning reef at Fighting Island (1 of 5 years). Median cumulative egg CPUEs were Island (Roseman, Manny, and others, 2011; Bouckaert and always low, only exceeding 5 eggs/mat at Sugar Island where others, 2014; Manny and others, 2015) and were collected CPUEs of 11.0 eggs/mat (in 2007) and 13.7 eggs/mat (2011) from this site in 2009, 2010, 2012, and 2014. Chronologi- were observed (table 3). cally, median lake sturgeon egg CPUEs for these years among Lake whitefish eggs were collected from all river regions all sites sampled at NE Fighting Island were 1.0, 0.33, 5.9, except Zug Island and Celeron Island from 2006 to 2014 and 9.0 eggs/mat, respectively. However, almost all of these (table 4). Spawning by lake whitefish was prevalent through- eggs were collected on the artificial reef. Median cumulative out the Detroit River and typically began within the first two egg CPUEs among the four reef sites closest to the shore weeks of November (mean onset temperature was 8.1 degrees (corresponding to reef treatments A–D from Roseman, Manny, Celsius [°C]) and continued into mid-December (mean ces- and others [2011]) were considerably greater: 22.6, 1.2, and sation temperature was 2.7 °C; table 5). River-wide, lake 40.2 for 2009, 2010, and 2012, respectively. The CPUE of whitefish egg CPUEs were generally intermediate to those lake sturgeon eggs among these four sites decreased in 2014 of walleye and suckers. Median cumulative egg CPUEs for (3.3 eggs/mat); however, this followed the 2013 construction a given year-region combination rarely exceeded 10 eggs/ of downstream extensions to the reef, which had a higher mat (table 4), but an exceptionally high density was observed median CPUE (117 eggs/mat). Lake sturgeon eggs were not at NE Fighting Island in 2014 (110 eggs/mat) and at NW collected from any other sites in the Detroit River during Fighting Island/Grassy Island in 2013 and 2014 (63.4 and this study. 47.9 eggs/mat, respectively).

Table 2. Median cumulative catch–per–unit effort (CPUE) of sucker eggs collected during spring egg mat sampling in the Detroit River, 2005–14. Italics denote sampling season ended early because of gear loss and values may be underestimated.

[–, site was not sampled]

Region Sucker CPUE (eggs/mat)—Detroit River (in downstream order) 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Peche Island – – – 1.0 – – – – – – Belle Isle 6.1 2.2 0.29 3.1 – 0.37 1.0 – 0.24 0.89 Debris mound adjacent – – – – – – 0 – 0 – to Joe Louis Arena Fort Wayne – – 0 0.33 – – – – 2.0 – Zug Island – – 2.7 15.0 – – – – – – NE Fighting Island – – 2.4 10.8 6.8 8.4 7.0 1.1 58 61 NW Fighting Island/ – – 0.49 0.53 – – 16.1 – 10 0.48 Grassy Island SW Fighting Island/ – – 0 0 – – – – – – NE Grosse Ile SE Fighting Island – – 3.0 0 – – – – – – N Livingstone Channel – – 0.33 0 – – 0 – 0.33 0 Trenton Channel – – 0 2.2 – – – – – – Bois Blanc Island/ – – 1.5 0.73 – – 6.3 – 3.7 6.0 Hole–in–Wall Sugar Island – – 9.3 0 – – 0.67 – 0 0 Celeron Island – – 0 – – – – – – – 8 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

Table 3. Median cumulative catch–per–unit effort (CPUE) of trout–perch eggs collected during spring egg mat sampling in the Detroit River, 2005–14. Italics denote sampling season ended early because of gear loss and values may be underestimated.

[–, site was not sampled]

Region Trout-perch CPUE (eggs/mat)—Detroit River (in downstream order) 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Peche Island – – – 0 – – – – – – Belle Isle 0 0.04 0.19 0 – 0 0.05 – 0 0.33 Debris mound adjacent – – – – – – 0 – 0 0 to Joe Louis Arena Fort Wayne – – 0 0 – – – – 0 – Zug Island – – 0 0 – – – – – – NE Fighting Island – – 0 0.26 0.74 0.29 1.7 1.0 4.6 0.40 NW Fighting Island/ – – 0 0 – – 0.53 – 0 0 Grassy Island SW Fighting Island/ – – 0 0 – – – – – – NE Grosse Ile SE Fighting Island – – 0 0 – – – – – – N Livingstone Channel – – 0 0 – – 0 – 0 0 Trenton Channel – – 0 0 – – – – – – Bois Blanc Island/ – – 0.29 0 – – 2.7 – 1.3 1.3 Hole–in–Wall Sugar Island – – 11 0 – – 14 – 0 0 Celeron Island – – 0 – – – – – – –

Table 4. Median cumulative catch–per–unit effort (CPUE) of lake whitefish eggs collected during fall egg mat sampling in the Detroit River, 2006–14. Italics denote sampling season ended early because of gear loss and values may be underestimated.—Continued

[–, site was not sampled]

Region Lake whitefish CPUE (eggs/mat)—Detroit River (in downstream order) 2006 2007 2008 2010 2011 2012 2013 2014 Peche Island 1.2 1.2 – – – – – – Belle Isle 1.7 8.7 – 6.2 – 11.1 0.6 0.87 Debris mound adjacent to Joe Louis Arena – – – – – 1.0 – 3.7 Fort Wayne – 0.7 – – – 19 0 – Zug Island – 0 – – – – – – NE Fighting Island 7.8 6.0 3.7 3.2 17 8.4 3.8 110 NW Fighting Island/Grassy Island 0.29 6.5 – – – – 63 48 SW Fighting Island/ 1.4 2.6 – – – – – – NE Grosse Ile SE Fighting Island 0.33 0.33 – – – – – – N Livingstone Channel 3.4 2.3 – – – – 0 1.0 Results 9

Table 4. Median cumulative catch–per–unit effort (CPUE) of lake whitefish eggs collected during fall egg mat sampling in the Detroit River, 2006–14. Italics denote sampling season ended early because of gear loss and values may be underestimated.—Continued

[–, site was not sampled]

Region Lake whitefish CPUE (eggs/mat)—Detroit River (in downstream order) 2006 2007 2008 2010 2011 2012 2013 2014 Trenton Channel 0 0.63 – – – – – – Bois Blanc Island/Hole–in–Wall 5.3 8.2 – – – 3.7 8.0 28 Sugar Island 4.3 6.2 – – – 3.7 – 25 Celeron Island 0 – – – – – – –

Table 5. Water temperatures corresponding to the onset and cessation of egg collections in the Detroit River, 2005–14. Reported values are daily mean water temperatures in degrees Celsius.

[–, eggs of this species were not collected during sampling; DNS, did not sample; NA, onset or cessation was missed and there- fore temperature was not available; %, percent; CI, confidence interval]

Walleye Sucker (large) Trout-perch Year Onset Cessation Onset Cessation Onset Cessation 2005 NA 11.5 5.8 15.7 – – 2006 NA 13.0 9.0 19.0 11.8 13.0 2007 6.5 13.4 3.8 16.1 9.0 13.0 2008 5.6 10.7 10.2 14.5 10.2 13.8 2009 4.6 12.6 5.6 12.5 7.6 NA 2010 NA 11.7 NA 20.3 NA 20.0 2011 5.1 11.5 9.8 14.4 8.2 18.9 2012 NA NA NA NA NA NA 2013 5.4 12.4 7.8 10.6 7.8 16.5 2014 4.8 12.3 8.2 14.2 8.3 17.8 Mean 5.3 12.1 7.5 15.3 9.1 16.1 95% CI 4.8–5.9 11.6–12.7 6.0–9.1 13.3–17.2 8.0–10.2 14.0–18.3 Sucker (small) Lake sturgeon Lake whitefish Year Onset Cessation Onset Cessation Onset Cessation 2005 5.8 12.8 – – DNS DNS 2006 6.2 12.0 – – NA 2.9 2007 13.4 17.1 – – 8.9 1.7 2008 10.9 12.2 – – DNS DNS 2009 10.6 NA 10.6 12.5 9.5 3.8 2010 13.3 19.9 13.3 12.9 8.3 0.3 2011 11.5 14.5 – – NA NA 2012 NA NA 9.3 13.1 NA 4.8 2013 7.8 14.9 – – 6.0 NA 2014 7.5 17.8 8.2 11.5 7.6 NA Mean 9.7 15.1 10.3 12.5 8.1 2.7 95% CI 7.8–11.6 13.2–17.1 8.2–12.5 11.8–13.2 6.9–9.3 1.2–4.2 10 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

In the spring, walleye eggs were the earliest to be col- deposition did not differ substantially between artificial reef lected with a mean onset date of April 8, corresponding with sites and adjacent sites with natural substrate at Belle Isle. a mean water temperature at onset of 5.3 °C (table 5). Collec- Since 2008, the greatest proportion of fish egg sam- tions of walleye eggs were generally followed by large sucker pling effort in the Detroit River has been in the NE Fighting eggs (mean onset April 21; 7.5 °C), trout-perch eggs (April 28; Island region. The spatial relation was examined between egg 9.1 °C), small sucker eggs (April 28; 9.7 °C), and lake sturgeon deposition and position relative to the location of the artificial eggs (May 1; 10.3 °C). Walleye also were the earliest species to spawning reef by estimating egg CPUEs among sites similarly complete spawning, with an average cessation date of May 7 distanced upstream and downstream from the reef (fig. 5). and water temperature of 12.1 °C (table 5), followed by lake Lake sturgeon exhibited the greatest use of the reef relative sturgeon (May 16; 12.5 °C), sucker species with large eggs to sites upstream or downstream and showed the strongest, (May 27; 15.3 °C), sucker species with small eggs (May 29; positive postconstruction response. Lake sturgeon eggs were 15.1 °C), and trout-perch (June 2; 16.1 °C). Lake sturgeon not collected at any Fighting Island sites prior to the construc- eggs were collected over a shorter duration than eggs of the tion of the reefs in 2008 but were collected on reef sites in other taxa, with 95 percent of the eggs being collected over an 2009 (1.9 eggs/mat), 2010 (0.76 eggs/mat), 2012 (17.5 eggs/ annual mean of 15.5 days (fig. 3). The relation of egg collec- mat), and 2014 (3.3 eggs/mat); additionally, smaller CPUEs of tions to temperature was strongest for walleye, with 95 percent lake sturgeon eggs were collected among sites averaging 135 confidence intervals for the mean temperatures of both onset m downstream from the Fighting Island reefs in 2009 (0.49 and cessation among all years spanning only 1.1 °C (table 5). eggs/mat), 2012 (1.5 eggs/mat), and 2014 (1.0 eggs/mat). Fish egg CPUEs generally were similar among reef and Trout-perch showed evidence of increased egg deposition on nonreef sites in the Belle Isle region (fig. A4 ), where a fish- the Fighting Island reef following its construction in 2008 (fig. 5). spawning reef was constructed in 2004. With the exception of Among all years following the reef construction (2009–14), lake whitefish in fall 2012, where the median cumulative egg trout-perch egg CPUEs were greatest on the Fighting Island CPUE among three artificial reef sites was 26.9 eggs/mat com- reef sites (1.2 eggs/mat/year), slightly exceeding those among pared to zero for a single adjacent natural substrate site, egg sites averaging 135 m downstream (0.88 eggs/mat/year).

60 EXPLANATION Error bar Detroit River

50 Saint Clair River

40

30

20 Duration of egg collection, in days

10

0 Walleye Sucker (large) Lake sturgeon Sucker (small) Trout-perch Taxa

Figure 3. Average duration of egg collections of lithophilic-spawning fishes in the Detroit and Saint Clair Rivers for years in which the onset and cessation of spawning were detected. Error bars denote ±1 standard error. Results 11

A. Belle Isle B. Fighting Island

8 8 Walleye Walleye

6 6

4 4

2 2

0 0

8 8 Catostomidae spp. Catostomidae spp. -scale) e 6 6

4 4

2 2

Mean CPUE (eggs/mat, log 0 0

8 8 Lake whitefish Lake whitefish -scale) 6 e 6

4 4

2 2

0 Mean CPUE (no./mat, log 0 2006 2008 2010 2012 2014 8 EXPLANATION Trout-perch Reef 6 Natural Reef extensions 4 Figure 4. Cumulative mean catch-per-unit effort

(CPUE) of eggs on mats sampled on or near the artificial 2 reef complex off the northeastern shores of A, Belle Isle 2005–14; and B, Fighting Island 2006–14. Symbols 0 represent the yearly means of the loge (total eggs collected + 1) per mat among sampling sites. In A, open 8 circles correspond to sites on the reefs and shaded Lake sturgeon

circles correspond to sites on natural substrate at the 6 head of Belle Isle. In B, open circles correspond to sites sampled on the reefs (2009–14) or where the reefs 4 were later built (2006–8). Shaded triangles describe the

cumulative mean loge-CPUE of eggs sampled on reef extensions installed immediately downstream from the 2 original reefs, summer 2013. In both A and B, error bars denote ±1 standard error. Note that not every region was 0 sampled in each year. 2006 2008 2010 2012 2014 12 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

8 2 Walleye Lake sturgeon

6

4 1

2

0 0

5 5 Catostomidae spp. Lake whitefish

4 4 -scale) e

3 3

2 2

1 1 Mean CPUE (eggs/mat, log 0 0 –150 0 135 450 2 Mean distance downstream from reefs, in meters Trout-perch

1

0 –150 0 135 450 Mean distance downstream from reefs, in meters

Figure 5. Cumulative mean catch-per-unit effort (CPUE) of eggs on mats sampled in the vicinity of the artificial reef complex at the

head of Fighting Island. Symbols represent the yearly means of the loge (total eggs collected + 1) per mat among sampling sites both upstream and downstream from the reefs, as well as on the reefs themselves. Shaded triangles and open circles correspond to preconstruction and postconstruction of artificial spawning reefs, respectively (that is, before and after summer 2008), and the line describes the mean of the time series. Note that not every distance was sampled each year. Walleye, Catostomidae spp., and lake whitefish showed at the reef sites (23.8 eggs/mat/year) and at sites averaging similar spatial patterns in egg CPUEs preconstruction and 135 m downstream (27.6 eggs/mat/year), but this pattern was postconstruction of the Fighting Island reef (fig. 5). Although essentially the same before construction of the reef (fig. 5). median egg CPUEs on the reef were greatest for walleye, Compared to sites sampled upstream (11.0 eggs/mat/year ) more eggs were collected from the upstream sites than on the and downstream (21.0 eggs/mat/year) from the Fighting Island reefs. The average values of annual median walleye egg CPUE reef, lake whitefish egg CPUEs appeared depressed at sites on (that is, back-transformed from loge-CPUE in fig. 5) among sampling sites averaging 150 m upstream from the Fighting the reefs (5.6 eggs/mat/year) among all years, although this Island reef were greater (100 eggs/mat/year) than at sites on may not be significant because of interannual variability. The the reef (31.1 eggs/mat/year) or sites averaging 135 m down- Fighting Island reef was enlarged on the downstream side in stream from the reefs (31.4 eggs/mat/year), although interan- summer 2013, and this new area was heavily utilized by lake nual variability was high. Sucker egg CPUEs were greatest sturgeon in 2014 (117 eggs/mat; fig. 4b). Results 13

Saint Clair River Saint Clair Middle Grounds in 2013, where 2.3 eggs/mat were collected. Other notable catches of large sucker eggs occurred The CPUEs of fish eggs in the Saint Clair River were at the North Channel Saint Clair River (end)/Chenal A Bout much lower than those in the Detroit River; nonetheless, eggs Rond region (2.0 eggs/mat in 2011) and at Algonac (1.9 and of at least one species were collected among all regions of the 1.8 eggs/mat in 2011 and 2013, respectively). Saint Clair River that were sampled throughout the time series. Unlike the Detroit River, trout-perch and small sucker The greatest walleye egg CPUEs throughout the time series eggs were rarely collected in the Saint Clair River. Only five were observed in the Algonac region, where median cumula- small sucker eggs were identified among all regions sampled tive CPUE peaked in 2013 (36.3 eggs/mat) and was also high in 2013 and 2014. Trout-perch eggs were only collected in in 2011 (10.1 eggs/mat). The third greatest catch of walleye 2011; however, CPUEs in the North Channel Saint Clair River eggs occurred at Fawn Island in 2013, where 8.2 eggs/mat (end)/Chenal A Bout Rond region were extremely high at were observed. No other local annual walleye catches exceed- 107 eggs/mat. Trout-perch eggs were also collected among ing 5.0 eggs/mat were observed in the Saint Clair River. three sites at Algonac, with a median cumulative CPUE of Throughout the time series, collections of walleye and 0.79 eggs/mat. lake sturgeon eggs were similar in magnitude (1,085 and Lake whitefish eggs were collected on two occasions 975 total eggs, respectively) but varied greatly in their areal at sites in the Saint Clair Middle Grounds region. In 2012, extents. From 2010 to 2014, lake sturgeon eggs were only three lake whitefish eggs were collected (median CPUE of collected at 4 of the 14 regions, while walleye eggs were 0.26 eggs/mat), and in 2014, one egg was collected (0.15 eggs/ collected in every region in at least one year except the coal mat). These collections are the first accounts of lake whitefish cinder pile in North Channel Saint Clair River or North Channel eggs from the Saint Clair River. Saint Clair River (end)/Chenal A Bout Rond. The majority Five regions were sampled in all years from 2010 to 2014 (88.5 percent) of lake sturgeon eggs sampled from the Saint in the Saint Clair River (fig. 6). Among all taxa, 2011 and Clair River were collected at the coal cinder pile (fig. 6). The 2013 tended to support the greatest egg CPUEs at each region. CPUE peaked at the coal cinder pile in 2011 at 161 eggs/mat, Walleye and large sucker egg CPUEs showed very similar which is more than four times greater than the highest densi- temporal patterns within each of the regions of Port Huron, ties of lake sturgeon eggs collected at the Fighting Island reef Saint Clair Middle Grounds, and Algonac. in 2012. High CPUEs of lake sturgeon eggs were also col- The temporal order in which fish taxa spawned in the lected in 2010, 2013, and 2014 with 45.7, 57.0, and 19.7 eggs/ Saint Clair River was similar to that of the Detroit River, mat, respectively, at the coal cinder pile (fig. 6). although spawning began later for all species. Walleye were Sixty-two lake sturgeon eggs were collected in a trial 24-hour, three-mat-gang set during construction of the Middle the first to begin spawning, with a mean onset of April 17 Channel Saint Clair River reef (May 30, 2012), but there are among years in which the onset was captured (mean onset ° no other fish egg data for 2012 because of reef construction. water temperature = 3.1 C; table 6). Mean onsets of large ° In the year following construction of the Middle Channel sucker eggs (May 3; 7.2 C) and lake sturgeon eggs (May 25; ° Saint Clair River reef, lake sturgeon eggs were collected in 11.4 C) followed. On average, collections of walleye eggs ° low CPUEs (1.4 eggs/mat); in 2014, no lake sturgeon eggs ceased May 20 (11.0 C), followed by lake sturgeon (June 8; ° ° were collected from this region. The only other collections of 14.5 C), and large sucker eggs (June 11; 14.9 C). The dura- lake sturgeon eggs in the Saint Clair River occurred in 2014, tions of spawning for each taxon were similar between the during which a median cumulative CPUE of 2.9 eggs/mat was Detroit and Saint Clair Rivers, and, as was observed in the observed among four sites sampled in the Saint Clair Middle Detroit River, lake sturgeon spawned over a shorter duration Grounds region, and a single lake sturgeon egg was collected in the Saint Clair River than the other taxa (fig. 3). Water among three sites at Port Huron (0.10 eggs/mat). temperatures at the onset of walleye spawning were signifi- Low CPUEs of large sucker eggs were observed from cantly colder in the Saint Clair River than the Detroit River every region of the Saint Clair River except Fawn Island, among years where the onset was captured by sampling in Middle Channel Saint Clair River (end), and the Lower both rivers (two-sided paired t-test; p = 0.04); however, water Main Shipping Channel Saint Clair River. Median cumula- temperatures at cessation of spawning by walleye were not tive egg CPUEs seldom exceeded 1.0 eggs/mat, with the significantly different between rivers, and temperatures char- primary exception of 10.3 eggs/mat at Port Huron in 2010. acteristic of the onset and cessation of egg collections were not The second greatest CPUE of large sucker eggs was at the significantly different between rivers for any other taxa. 14 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14

10 8 8 12 Saint Clair Middle Grounds Port Huron 8 8 10 6 8 6 6 4 6 4 4 4 2

2 2 Suckers CPUE (eggs/mat) Suckers CPUE (eggs/mat) Walleye CPUE (eggs/mat) Walleye CPUE (eggs/mat) Walleye 2

0 0 0 0 ONTARIO 2010 2011 2012 2013 2014

5 Algonac Coal cinder pile 80 150 4

60 3 100 40 2 50 20

1 Suckers CPUE (eggs/mat) Walleye CPUE (eggs/mat) Walleye

Lake Sturgeon CPUE (eggs/mat) 0 2010 2011 2012 2013 2014 0 0 2010 2011 2012 2013 2014

0.3 0.6 Upper Middle Channel (and reef)

MICHIGAN 0.2 0.4

N

0.1 0.2 Walleye CPUE (eggs/mat) Walleye Suckers CPUE (eggs/mat) 0 5 KILOMETERS 0 0 0 5 MILES 2010 2011 2012 2013 2014 Lake Saint Clair

Figure 6. Densities of eggs collected 2010–14 at five regions sampled each year in the Saint Clair River. Catch-per-unit effort (CPUE) values are

the back-transformed mean loge (total eggs caught/mat + 1) among all sampled sites within a river region during the whole sampling season. For all regions except coal cinder pile, open circles correspond to walleye egg densities (left y-axis), and filled circles correspond to sucker egg densities (right y-axis). Error bars represent ±1 standard error.

Table 6. Water temperatures corresponding to the onset and cessation of egg collections in the Saint Clair River, 2010–14. Reported values are daily mean water temperatures in degrees Celsius, measured by boat among all sites.

[NA, onset or cessation was missed and therefore temperature was not available; %, percent; CI, confidence interval]

Walleye Sucker (large) Lake sturgeon Year Onset Cessation Onset Cessation Onset Cessation 2010 NA 12.1 7.4 19.5 10.9 17.4 2011 2.7 8.8 5.1 15.8 10.7 13.4 2012 NA 13.1 7.4 14.8 13.1 14.8 2013 3.2 9.2 9.0 12.6 11.0 12.6 2014 3.3 11.6 7.3 11.8 11.2 14.3 Mean 3.1 11.0 7.2 14.9 11.4 14.5 95% CI 2.7–3.4 9.3–12.6 6.0–8.5 12.3–17.6 10.5–12.3 12.9–16.1 Discussion 15

Discussion stream. Similarly, Muth (1975) hypothesized that in Twelve- pole Creek, West Virginia, trout-perch spawned at night in This report provides a contemporary account of where shallow riffles, usually less than 0.45 m deep. In contrast to spawning occurs by ecologically and economically important these studies, the findings in this report and those of Muth and lithophilic-spawning fish species in the Detroit and Saint Clair others (1986) highlight the potential importance of deeper, Rivers—a key first step in tracking the success of fish habitat swifter flows to trout-perch reproduction in the SCDRS. restoration progress in the SCDRS. Historically, the Detroit It was found that lake whitefish spawn throughout the and Saint Clair Rivers were important for fish spawning and Detroit River in the fall, which is congruent with historic subsequent recruitment (Goodyear and others, 1982), but the depictions of Detroit River lake whitefish spawning runs habitats and flow regimes therein have been highly altered extending from the river mouth up to Belle Isle (Goodyear and (Manny and others, 1988; Bennion and Manny, 2011; Hondorp others, 1982). The consistent sampling of lake whitefish eggs and others, 2014), and this has contributed to multiple declines in the Detroit River underscores the continued recovery of this of fisheries and limited their recovery (Smith, 1972; McClain stock from its collapse in the early 1900s. Additionally, it is and Manny, 2000; Roseman and others, 2007; Manny and promising that some of the greatest lake whitefish egg CPUEs others, 2010). Through the large-scale survey of fish spawning that were observed over the time series occurred in 2011–14 in these two rivers, a better understanding was gained of how (table 4). these connecting channels currently contribute to the structure In the SCDRS, lake sturgeon showed the greatest discre- and restoration of fish communities in the SCDRS and in tion in choosing when and where to spawn. Their eggs were adjacent Lakes Huron and Erie. collected almost exclusively on artificial reefs, but not on It was found that walleye and an unresolved diversity every reef each year. The apparently greater spawning discre- of sucker species (Catostomidae spp.) spawn throughout the tion shown by lake sturgeon in the SCDRS, as compared to Detroit and Saint Clair Rivers in the spring. Aside from the walleye, suckers, and lake whitefish, is likely influenced by recent documentation of white sucker spawning at Belle Isle their respective life histories and spawning strategies. Lake (Manny and others, 2010), knowledge of historic sucker (and sturgeon is a long-lived species that matures late (males age most other species) spawning activity in the SCDRS was 12–15 years, females age 18–27 years), and individuals poten- previously limited to collections of fish larvae (Goodyear tially spawn several times throughout their adult lives over the and others, 1982; Hatcher and Nester, 1983; Muth and oth- span of multiple decades (see Peterson and others [2007] for a ers, 1986). For walleye, limited previous accounts suggested summary of lake sturgeon ecology). As a result, lake sturgeon spawning in the Detroit River was confined to the lower tend to be exposed to a greater diversity of spawning condi- reaches around Stony and Bois Blanc Islands, the Livingstone tions throughout their lives than other lithophilic-spawning and Amherstburg Channels, and the lower Trenton Channel fish in the SCDRS. Thus, when suitable spawning habitat or extending to the western shore of Sugar Island (Goodyear and environmental conditions are not detected, the energetic sav- others, 1982). It was also thought that walleye may not even ings of not spawning and (or) resorbing gametes, which take spawn in the Saint Clair River proper, and that adult walleye several years to develop (Roussow, 1957), may exceed the in the Saint Clair River were migrating to and from tributaries benefits of spawning under conditions where early life stages to the SCDRS and the western basin of Lake Erie (Goodyear of lake sturgeon are not likely to survive (that is, mitigates and others, 1982). This report is the first account of collections losses of reproductive fitness because of poor year classes). of walleye eggs from the Saint Clair River since Muth and The immediate spawning responses by lake sturgeon to the others (1986), who collected only a single walleye egg during construction of the Fighting Island and Middle Channel Saint sampling in 1983–84. Clair River reefs suggest lake sturgeon are very aware of The collections of trout-perch eggs were somewhat unex- their environment, and the hypothesis that low availability of pected given that the sampling sites tended to be in deep water suitable spawning habitat remains a limiting factor to their near the main flow of the rivers; however, Muth and others reproduction is supported. (1986) collected trout-perch eggs at depths ranging from 2.7 In contrast to lake sturgeon, walleye, lake whitefish, to 13.7 m in the Saint Clair River and from 3.7 to 8.2 m in the and suckers spawned in nearly every region of each river Detroit River in 1983 and 1984, primarily over mixtures of in all years and on both reef and nonreef substrates. For sand and gravel substrate. In other systems, trout-perch have these comparatively shorter-lived species, less judicious been observed to spawn in shallow depths, but little else is gametic resource allocation may be an alternative strategy known about their spawning behavior. Magnuson and Smith to increase reproductive fitness in the SCDRS. Compared to (1963) observed trout-perch exhibiting broadcast spawning lake sturgeon, eggs of walleye and suckers were collected along the shores of and in tributaries to Lower Red Lake, over a wider range of spawning conditions both spatially and Minnesota, in less than 1 m of water. They found that spawn- temporally in the spring (fig. 3) within a given year. However, ing took place in one tributary within 13 cm of the surface although high egg CPUEs were observed for walleye, lake and was concentrated in shallow water near the edges of the whitefish, and suckers, the fact that many of these eggs are 16 Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14 spawned over substrate with little interstitial space to protect others, 2015). If coupled with three-dimensional hydrody- the deposited eggs means these high CPUEs do not necessarily namic transport modeling (Beletsky and others, 2007), such indicate successful reproduction (that is, egg survival or information could provide a greater depiction of egg transport recruitment). For example, some of the greatest walleye egg and settling. CPUEs were observed at the head of Belle Isle (fig. A4 and Next, careful consideration must be given to the influence table 1) where the natural river bottom consists mostly of clay of incubation time on egg mat collections and its interactions covered by coarse sand (Manny and others, 2010). Additional with water temperature and downstream drift. Estimates of high walleye and sucker egg CPUEs on natural substrates incubation time for walleye and white sucker eggs from 1982 at NE Fighting Island were over thin patches of small diam- to 1991 in the Valley River, Manitoba, Canada (Johnston eter gravel and sand on sculpted hard-pan clay (Roseman, and others, 1995), averaged 12.0 and 14.8 days, respectively, Manny, and others, 2011). Walleye and suckers in the SCDRS although water temperatures were not reported. Furthermore, have shown a generally consistent spatial pattern in their egg controlled laboratory experiments by Hamel and others CPUEs, thus substrate characteristics may not be the primary (1997) found that white sucker eggs raised below 16.6 °C driver of where they choose to spawn in the SCDRS. Walleye had incubation times of at least 11.3 days between deposition spawn over a wide range of substrates and microhabitats, and hatching. For comparison, the collections of large sucker with depth and flow velocity often being important predictors eggs in this study generally were between 7.5 and 15.3 °C of reproductive effort (Bozek and others, 2011). In the Saint in the Detroit River (table 5) and between 7.2 and 14.9 °C in Clair River, site-specific conditions favorable for spawning the Saint Clair River (table 6). For lake sturgeon, Kempinger may be similar between walleye and suckers because similar (1988) reports egg incubation durations ranging from 8 to temporal patterns are shown within each of the regions of Port 14 days in the Lake Winnebago system, Wisconsin; Smith Huron, Saint Clair Middle Grounds, and Algonac, which were and King (2005) report egg incubation durations ranging from sampled every year from 2010 to 2014 (fig. 6). Interestingly, 5 to 11 days in the Black River, Michigan; and Johnson and walleye eggs were never collected at the coal cinder pile in others (2006) report average incubation times of 6 days for North Channel Saint Clair River—a presumably preferable eggs reared at 16 °C, which is a warmer temperature than most substrate compared to sand and clay. It was noted that the of the lake sturgeon egg collections reported herein (tables 5 creation of reefs in both rivers has shown no obvious impact and 6). Multiple studies (Brooke, 1975; Brown and Taylor, on where walleye, lake whitefish, and suckers choose to spawn 1992) indicate that lake whitefish eggs deposited in the fall but has likely increased the survival of eggs deposited over incubate over winter. Thus, with the possible exception of lake them by decreasing rates of egg siltation, predation, or of sturgeon, weekly gear retrieval is a reasonable frequency to being washed downstream (Crane and Farrell, 2013). collect deposited eggs from egg mats before they hatch. In order for egg mat collection data to more accurately represent fish spawning in the SCDRS, many uncertainties Widespread spawning by numerous native indicator need to be addressed. First, laboratory studies to evaluate the fish species suggests improvement of spawning habitat in the influence of current velocity, substrate, and species-specific SCDRS that is reflective of environmental quality improve- egg characteristics on egg capture efficiency and retention may ments since the 1970s (Hartig and others, 2009); however, the inform correction factors that could be applied to egg mat data production of lithophilic broadcast spawning fish species in from this study. Alternatively, D-frame drift nets are a sam- the SCDRS is likely still limited by the availability of suitable pling gear that would alleviate losses of eggs during sampling spawning substrate. The construction of artificial reefs may be and gear retrieval, and when coupled with flow meters, could an effective tool toward the restoration of such habitat within also measure the volume of water sampled. However, such the Great Lakes (Manny and others, 2015; McLean and others, gear is more prone to fouling by masses of aquatic vegetation 2015), the availability of which may trigger the act of spawn- than egg mats and requires a buoy to keep the net upright. ing (as seen with lake sturgeon) or increase the survival of fish Experience in this study suggests that this is particularly eggs. To predict the potential for further restoration efforts to problematic in the Detroit and Saint Clair Rivers because of effectively address conservation objectives, future research high freighter and recreational angling boat traffic, and this is needed to estimate (1) the relation between observed fish was the impetus for the development of the buoy-less egg egg densities and other habitat characteristics (for example, mat sampling method (Roseman, Boase, and others, 2011). proximity to nursery habitats), and (2) the influence of natural Additionally, D-frame drift nets can only capture eggs in and artificial substrates in the SCDRS on fish egg survival. transit, whereas eggs can be directly deposited over egg mats Ultimately, this research offers a unique insight to fish use by spawning fish. Lastly, there have been recent advances of the SCDRS and their responses to restoration efforts, in three-dimensional measurements of water velocity in the providing new contemporary knowledge needed to guide SCDRS using acoustic Doppler current profiling (Fischer and fisheries management. References Cited 17

Summary Bennion, D.H., and Manny, B.A., 2011, Construction of ship- ping channels in the Detroit River—History and environ- mental consequences: U.S. Geological Survey Scientific The areal extent of lithophilic-spawning fish egg collections Investigations Report 2011–5122, 14 p. in the Detroit (2005–14) and Saint Clair (2010–14) Rivers was summarized. Cumulative catch-per-unit effort (CPUE) of eggs Bennion, D.H., and Manny, B.A., 2014, A model to locate collected per species per spawning season was calculated and potential areas for lake sturgeon spawning habitat construc- reported by river regions, and dates and water temperatures tion in the St. Clair–Detroit River system: Journal of Great of the onset and cessation of spawning were presented for the Lakes Research, v. 40, p. 43–51. primary taxa observed in each river. Walleye (Sander vitreus), lake whitefish Coregonus( Bouckaert, E.K., Auer, N.A., Roseman, E.F., and Boase, James, 2014, Verifying success of artificial spawning reefs clupeaformis), lake sturgeon (Acipenser fulvescens), suckers in the St. Clair–Detroit River System for lake sturgeon (Catostomidae spp.), and trout-perch (Percopsis omiscomaycus) (Acipenser fulvescens Rafinesque, 1817): Journal of Applied were found to spawn extensively throughout the Detroit and Ichthyology, v. 30, p. 1393–1401. Saint Clair Rivers. The CPUEs of walleye, lake whitefish, and sucker eggs were much greater in the Detroit River than in the Bozek, M.A., Haxton, T.J., and Raabe, J.K., 2011, Walleye and Saint Clair River, while lake sturgeon egg CPUEs were high- sauger habitat, in Barton, B.A., ed., Biology, management, est from the Saint Clair River. Walleye, lake whitefish, and and culture of walleye and sauger: Bethesda, Maryland, sucker eggs were collected from both reef and nonreef sub- American Fisheries Society, p. 133–197. strates from among the majority of sampling locations in both Brooke, L.T., 1975, Effect of different constant incubation rivers. In contrast, lake sturgeon eggs were collected mainly temperatures on egg survival and embryonic development on man-made, artificial fish spawning reefs in the Detroit and in lake whitefish Coregonus( clupeaformis): Transactions of Saint Clair Rivers. Collections of lake sturgeon eggs on artifi- the American Fisheries Society, v. 104, p. 555–559. cial, fish spawning reefs (Fighting Island Reef, Detroit River and Middle Channel Saint Clair River reefs) during postas- Brown, R.W., and Taylor, W.W., 1992, Effects of egg compo- sessment years, but not during preassessment years, suggests sition and prey density on the larval growth and survival of lake sturgeon were able to locate and use these structures for lake whitefish (Coregonus clupeaformis Mitchell): Journal their intended purpose. of Fish Biology, v. 40, p. 381–394. The response exhibited by lake sturgeon of spawning on Bruch, R.M., and Binkowski, F.P., 2002, Spawning behavior newly constructed reefs indicates that successful reproduction of lake sturgeon (Acipenser fulvescens): Journal of Applied by lithophilic-spawning fishes may be limited in the Saint Ichthyology, v. 18, p. 570–579. Clair-Detroit River System. Additionally, the fact that eggs of walleye, lake whitefish, and suckers were often collected over Bull, J.N., and Craves, Julie, 2003, Biodiversity of the Detroit natural substrates with little interstitial space to protect the River and environs—Past, present and future prospects, in deposited eggs from siltation, sedimentation, or downstream Hartig, J.H., ed., Honoring Our Detroit River: Bloomfield scouring, suggests that lack of suitable spawning habitat may Hills, Mich., Cranbrook Institute of Science, p. 141–169. continue to limit successful reproduction of these species Caswell, N.M., Peterson, D.L., Manny, B.A., and Kennedy, as well. G.W., 2004, Spawning by lake sturgeon (Acipenser fulves- cens) in the Detroit River: Journal of Applied Ichthyology, v. 20, p. 1–6. 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Prichard and others—Egg Deposition by Lithophilic-Spawning Fishes in the Detroit and Saint Clair Rivers, 2005–14—Scientific Investigations Report 2017–5003 ISSN 2328-0328 (online) https://doi.org/10.3133/sir20175003